Chapter 7 - Arduino - Options for Powering Your Board

hello and welcome to this introduction to Arduino in this chapter we'll summarize concepts of power and work discuss different options for powering your Arduino and summarize associated limitations this is the seventh chapter in a ten-part series developed for local hackerspace here in Tucson so far we've discussed volts amps and resistance next we'll start putting these concepts together to talk about power and work let's start with power a watt is a unit of power and when power is applied over a period of time on a system it performs work in this case we can see the power of a stream is putting pressure on the waterwheel fins to help the wheel overcome friction on its bearing and thus is doing work on the waterwheel overtime since we already have an understanding of our electrical circuit using water flow let's add power and work to this explanation but before we do that let's do a quick review we know that pressure generated by our water pump is the same as what voltage is to a battery the resulting water flow from the pump is what amperage is to an electrical circuit also we know that a waterwheel in this circuit will produce resistance to flow which is the same as a load in an electrical circuit finally using Ohm's law we know that if our pump generates one volt of pressure and the resulting current through the circuit is 1 amp then our waterwheel is generating 1 ohm of resistance powers the next term we'll add to this metaphor power is basically the pressure of water multiplied by the Associated current in your circuit and it's what helps the waterwheel overcome resistance to turning on its bearing power results from the work done by your circuit over a unit of time or one second in electrical circuits power results from multiplying voltage times current over time which is the same as volts times amps per second in other words 1 volt pushing one amp through your circuit over the course of one second is equal to 1 watt work results from power helping the waterwheel overcome friction through time so it's essentially the same as power multiplied by time another way of thinking of this is the power you exert over the course of the day to get work done electrically the unit of power is the Joule which results from multiplying 1 watt times 1 second so if my circuit takes 1 watt of power and we're running for 1 minute which is the same as 60 seconds the total work that would be done by my circuit is 60 joules just as with Ohm's law we can come up with visual mnemonic to remember the relationships between power current and voltage if you can remember that power is equal to current times voltage you can quickly come up with the other relationships just by doing a little bit of algebra or just by referring to this visual mnemonic since we have terms in the power equation that are common to Ohm's law we can use these relationships to come up with a couple other equations for power as shown here this requires that we do a little bit of algebra that I will go into here suffice it to say that electronic components are rated to handle a limited amount of power so it's helpful to know these equations as we'll demonstrate in a minute for a power rating example consider the fact that resistors are sized to handle a certain amount of power the smaller the size of the resistor the less power can handle as shown typical wattage sizes for resistors are 1/8 1/4 1/2 1 and - what's so this led to a question I had about resistors specifically what power rating for a resistor do I consider to be reasonable for a typical Arduino project say one involving standard LEDs again the electrical power dissipation of any resistor can be determined by one of these formulas to demonstrate this let's revisit an example we shared in a prior chapter in this circuit I know my resistor will drop 3 volts with a current flow of 9 milliamps so plugging in the numbers for a current and resistance into one of my power equations I can see that the power dissipation will be about one 37th of a watt through my resistor this is much smaller than 1/8 of a watt so a resistor with the smallest rating for power would work fine but I might want to purchase the next size up just to give my project a little bit of headroom in closing power gives us a way of packaging the voltage resistance and or current flowing through our circuit into one term known as Watts understanding of the particular components power capabilities and limitations helps us determine if it's appropriate for our circuit or if we need to scale it up so now that we have a basic understanding of power let's revisit our Arduino board up to this point we understand that we can power our Arduino off our computers USB plug through the large metal plug on the left we also know that each of our digital and analog pins can provide up to 5 volts of pressure to supply 20 milliamps continuously and up to 40 milliamps for short periods of time well now that we know the power equation another way of thinking about the capability of each of these pins is that they can each provide 100 milliwatts of power which is the same as 5 volts times 20 milliamps we also know that we can supply 200 milliwatts of power for short periods of time which is the same as 5 volts times 40 milliamps that's fine but what about this barrel jack here on the left and what about the power pins down here what are they for and what are their limitations we'll get into that next but just a quick note that in the next few slides I'll speak strictly in the context of voltage and current limitations keep in mind that if you want to know the Associated power ratings you can now calculate these easy enough through the power equation so I just quickly want to acknowledge these sites as my references for the following slides if I don't cover everything you need to know these are good resources for the same let's start with the power Jack shown here on the left and the VI in pin shown here at the bottom of the board both these inputs can accept between 6 to 20 volts but if the Arduino runs on five volts how's this possible that's thanks to this little voltage regulator shown here the voltage regulator can take this range of higher voltages and bring them down to a nice steady 5 volts which is what the Arduino is designed for however it's recommended that when using these power inputs that you actually restrict the input between 7 and 12 volts next let's talk about some of the power outputs associated with the power pins along the bottom of the board for starters let's restrict our discussion to the output available when we are powering the Arduino using a 5 volt USB input from our computer that input provides our Arduino with 500 milliamps of current at 5 volts we can tap that current through these 2 pins at either 3.3 or 5 volts of pressure depending on whether we use the 3.3 or 5 volt pin the 3.3 volt pin will allow us to tap up to 150 milliamps of current which is the limit of the 3.3 volt regulator on the board the 5 volt pin will deliver up to 400 milliamps of current but why am I not getting the full 500 milliamps offered by my USB power supply the reason is that the 500 milli amps are being shared by all the devices on the board not just the headers so the associated loads are causing the current to drop before it gets to your 5 volt power pin with respect to the barrel jack input we can provide up to one amp of current to the board in this case the capabilities of our 5 volt pin is increased from four hundred to nine hundred milliamps whereas the 3.3 volt pen still can only supply us with a maximum 150 milliamps again it's okay for us to provide a higher voltage through the barrel jack because of the onboard voltage regulator however providing more than seven volts will cause the regulator to work harder and get hot this produces something called thermal limiting which results in the maximum available current through that 5 volt pin to drop as such that nine hundred milliamps is specific to a seven volt power supply if you tried pushing nine volts you drop the current to about half of what would be available through seven volts and if you increase the power supply to 12 volts the available current would be about 1/4 so just keep this in mind when selecting your power supply finally since this pin taps the barrel jack before the voltage regulator we can tap into the actual voltage provided by the input to that barrel jack - about 1/2 a bowl we can also source about one amp through the ein pin this will give us the same performance on the three point three and five volt pins as if we were powering the Arduino from the barrel jack note that these power inputs also power our GPIO pins remember that these are designed to source about 20 milliamp spur pin with the peak of 40 milliamps for short periods of time however the microcontroller the channels power to these pins can only handle a maximum of 200 milliamps total for all your pins as such you don't want to draw 20 milliamps from all your GPIO pins at the same time or you risk damaging your chip finally note that it is possible to power your Arduino through the 5 volt pen but keep in mind that this will bypass your voltage regulator as such this is not advised unless you really know what you're doing well up to now we've discussed attaching components to the GPIO pins what do I do if my component requires more than 20 milliamps advised for these pins or the sum total is greater than 200 milliamps that can be channeled by our microcontroller this is where that 5 volt pen comes in by making four hundred to nine hundred milliamps available through that pin I can hook it up to the power rail of a breadboard where I can attach and power those other components safely in fact when you purchase a shield it typically gets its power from that five volt pen in order to avoid the limitations associated with powering off the GPIO pins with respect to wall warts a common question is what should you look for when selecting one for your board the short answer is you want one that provides an output of seven to twelve volts direct current and that can source a minimum 250 milliamps or more the long answer is outlined in the following bullets keep in mind that power supply voltages above seven volts will offer less current due to the thermal limiting of the voltage regulator on your board and make sure that your plug is Center positive most power supply plugs I've come across are sent are positive but I have seen a few that are reversed so don't take this for granted so that just about does it for this chapter in the next chapter I'll go over how motors work discuss different kinds of motors and demonstrate how we can use pulse width modulation and specific functions in the Arduino software to control motors in addition I'm in the process of preparing some demonstrations on how to power your Arduino using solar power I'm also experimenting with running an Arduino off an old turntable motor converted to a generator and a Jensen toy steam engine not that this is practical in the lease but just because I want to see if it can be done more on that later if you want to be informed of updates please consider subscribing and thank you for watching [Music]

Channel: Modest Maker

Views: 15,545

Rating: 4.9405203 out of 5

Keywords: arduino, wall wart, powering, beginner, xerocraft, hans, huth, power limitations, arduino watts

Id: mTHwa_UCYMQ

Length: 13min 10sec (790 seconds)

Published: Sun Oct 15 2017